1. Field of the Invention
The present invention relates to a method and apparatus for Physical Downlink Control Channel (PDCCH) allocation in a wireless communication system, and more particularly, to a method and apparatus capable of reducing power consumption and computing complexity.
2. Description of the Prior Art
Long Term Evolution wireless communication system (LTE system), an advanced high-speed wireless communication system established upon the 3G mobile telecommunication system, supports only packet-switched transmission, and tends to implement both Medium Access Control (MAC) layer and Radio Link Control (RLC) layer in one single communication site, such as in base stations (Node Bs) alone rather than in Node Bs and RNC (Radio Network Controller) respectively, so that the system structure becomes simple.
However, to meet future requirements of all kinds of communication services, the 3rd Generation Partnership Project (3GPP) has started to work out a next generation of the LTE system: the LTE Advanced (LTE-A) system. Carrier aggregation (CA), where two or more component carriers are aggregated, is introduced into the LTE-A system in order to support wider transmission bandwidths, e.g. up to 100 MHz and for spectrum aggregation. In the LTE-A system, a user equipment (UE) uses multiple component carriers to establish multiple links with a network terminal for simultaneously receiving and transmitting on each component carrier, so as to enhance transmission bandwidth and spectrum aggregation.
The network terminal configures a plurality of carriers to a UE via a radio resource control (RRC) message. After CA is configured, the UE receives Physical Downlink Shared Channels (PDSCHs) on a plurality of configured downlink component carriers. Besides, the prior art further proposes to monitor a Physical Downlink Control Channels (PDCCHs) on other downlink component carriers, for acquiring related scheduling information, i.e. downlink assignment or uplink grant, to perform data reception or transmission. In other words, PDSCH and PDCCH may be carried on different component carriers. Therefore, within the configured downlink component carriers, part of component carriers may only carry PDSCHs, and not carry PDCCHs; while another part of component carriers simultaneously carry PDSCHs and PDCCHs. In such a situation, the UE can acquire the scheduling for all the configured component carriers by merely monitoring PDCCHs on part of the component carriers. As a result, power consumption or requirements for computing capability can be reduced, because requirements for the computing capability mainly result from different carriers using different encoding methods, and thus the more the monitored component carriers are, the more complex the required blind decoding computing is. Correspondingly, requirements for computing capability can be reduced by reducing an amount of the monitored component carriers.
As can be seen from the above, by carrying PDSCHs and PDCCHs on different component carriers and transmitting PDCCHs only on part of component carriers, the amount of the monitored component carriers is reduced, and power consumption or requirements for computing capability can be reduced. However, this method still has some potential for improvement under some circumstances. For example, when a transmission fails and a retransmission is performed, packets for the retransmission are only transmitted on the original carrier. Therefore, in theory, the network terminal only needs to transmit scheduling information required for the retransmission on one PDCCH. However, according to the prior art, the UE still needs to monitor all PDCCHs, since the UE does not know the scheduling information is transmitted on which PDCCH, causing unnecessary power consumption.
Therefore, how to further reduce power consumption or requirements for computing capability for CA has become an issue in the industry.